1. Field of the Invention
The present invention relates to a process for fabricating a magnetic disk using a thin film of a ferromagnetic metal suited for high density magnetic recording as the magnetic recording medium.
2. Prior Art
In the magnetic disks using rigid substrates, as compared with the conventional coated type magnetic disks, the surface smoothness of a disk has been more severely pursued to realize high-density recording. This applies, more particularly, to the so-called thin-film magnetic disks such as sputtered disks and plated disks. However, as the surface of the disk achieves a further smoother surface, there arises a problem of unfavorable contact between the magnetic head and the magnetic disk . That is, the magnetic head sticks, or in other words, is adsorbed to the magnetic disk upon resting it on a magnetic disk. This phenomenon occurs due to the presence of moisture or lubricants which are adsorbed to the surface of disk. To overcome this problem, it has been proposed to provide, on the surface of the magnetic disk substrate, a fine pattern of concentrical circles along the periphery of the substrate. Accordingly, a so-called texturing has been applied to magnetic disk substrates to develop fine irregularities in such a manner to reduce surface adsorption and to impart magnetic anisotropy to the magnetic film along the peripheral direction of the disk. In the proposed processes, texturing has been carried out by using a polishing tape comprising a polyester base tape having bonded and fixed thereto abrasive grains of alumina, or a polishing solution comprising abrasive grains of alumina, silicon carbide, etc., being dispersed in a solution.
With increasing magnetic recording density, on the other hand, it is desired to lower the flying height of the non-contact type magnetic head, i.e., to bring the magnetic head closer to the magnetic disk and to thereby achieve a higher signal sensitivity when making a record reproduction, This inevitably requires that the surface roughness of the disk substrate is minimized.
However, this requirement could not be fulfilled by polishing a magnetic disk substrate with a polishing tape having fixed thereon alumina abrasive grains. When a magnetic disk substrate was textured with such a polishing tape, minute protrusions in addition to the concentrical grooves were found irregularly on the surface. Accordingly, the magnetic head frequently collided against the protrusions upon shortening the flying height of the magnetic head, leading to a frequent occurrence of a so-called "head-hit". Thus, it was not possible to lower the magnetic head over the disk to too large an extent. On the other hand, however, too slight a texturing as to cause no head-hit results in too smooth a surface as to being about serious problem of head sticking.
In polishing the substrate using a polishing solution having dispersed therein alumina abrasive grains, there also occurred problems such as the formation of protrusions as mentioned above and the anchoring of alumina grains into the surface of the substrates, which gave protrusion-like effects. In this case again, it was not feasible to lower the magnetic head over the substrate to achieve a shorter flying height. It was possible, though, to suppress the formation of the protrusions on the surface of the substrate by shortening the processing duration or by lowering the pressure during the texturing, but this time, there inevitably occurred the problem of sticking of the magnetic head.